The applications long-term objective is to investigate neurodocrine changes responses for age-related loss of reproduction. The specific aims of this application are to use the techniques of high performance liquid chromatography with electrochemical detection and radioimmunoassay to determine age related changes in the release of catecholamines, serotonin, and luteinizing hormone and prolactin. The data on the release of neurotransmitters will be correlated with changes in serum levels of luteinizing hormone and prolactin. Changes in these parameters will also be determined in old acyclic animals. Role of gamma amino butyric acid in aged-related changes in luteinizing in old acyclic animals. Role of gama amino butyric acid in age-related changes in luteinizing hormone secretion and its interaction with norepinephrine will be test in young and aging animals. Changes in the response of neurotransmitters to prolonged exposure to estradiol will be determined by monitoring neurotransmitter release in young cycling animals. Similarly, the involvement of catecholamines in progesterone-induced reinitiation of estrous cycles in middle -aged persistent estrus animals will be examined. Patterns of neurotransmitters and hormone release will also be determined in old animals after induction of estrous cyclicity. The data collected will explain the involvement of neurotransmitters in normal reproductive cycles and in-age related changes in cyclicity. These data will be new and will add to our knowledge of the neuroendocrine involvement in loss of reproductive cyclicity in aging.